The present invention relates to an electrical appliance, and more particularly to an electrical appliance which is provided with corona discharge generating means for removing static electricity.
Generally, when an electrical appliance is used, static electricity is generated to some extent or other in places where friction occurs. To illustrate the case of an electric vacuum cleaner, when the dust is sucked, the dust is sucked through an intake port, passes through an extension pipe and a hose, and enters a dust case. The collision and friction of the dust with internal walls of the extension pipe and the hose take place repeatedly, and static electricity is generated as a result. In addition, when the dust is sucked into the dust case as well, static electricity is similarly generated due to the collision and friction with the inner wall of the dust case.
In cases where the material of the parts where static electricity occurs is a metal, when the operator touches those parts, he receives a large electric shock. This is attributable to the fact that, as compared with cases where static electricity is generated in a plastic material, even if the potentials of static electricity are identical, the metallic material is electrically conductive, so that all the charge accumulated in the metallic material is induced. On the other hand, since the plastic material is basically nonconductive, the induction of the charge does not take place so that an electrical shock is small. For this reason, conventional electrical applicances are provided with the following measures against static electricity:
(1) A wire which is exclusively used for grounding is provided, extending from a portion where static electricity is generated to the ground to constantly remove electrostatic electricity.
(2) An arrangement is provided such that the operator is constantly kept in contact with a portion where static electricity is generated to remove static electricity through the human body, or the potential of the human body is made identical with that of the portion where static electricity is generated to prevent the operator from being subjected to an electrical shock.
(3) A conductive member is suspended from the apparatus to the floor to remove static electricity.
(4) To remove static electricity, a wire is provided from a portion where static electricity is generated to an outer casing such as a housing of an electric blower, i.e., a member which is disposed adjacent to an energized conductive material and sufficiently has the effect of grounding. In this case, a resistor (in which a high resistance value of 15 M.OMEGA. or the like is used in an embodiment) is provided in the aforementioned wiring to ensure that a very small amount of current flows even if the insulation level is destroyed due to deterioration of insulation or the like of the electric blower and a short-circuiting occurs as a result.
The above-described prior art solutions to static electricity are fraught with various problems such as those described below.
With reference to the prior art (1) in which a special wire for grounding is provided, extending from the portion where static electricity is generated to the ground, this measure can be adopted relatively easily in the case of an installed (fixed) type. However, in the case of a mobile apparatus such as an electric vacuum cleaner, it is necessary to use a power cord with a grounding wire and to connect the same with the grounding. Athough the provision of such a power cord with a grounding wire is influenced by the power source, there are many cases where the provision is difficult. In addition, there is a possibility that the apparatus is operated without using the grounding, so that there is the problem of safety in addition to the handling efficiency.
In the arrangement of the prior art (2) in which the operator is constantly kept in contact with the portion where static electricity is generated, in a state in which an insulating material such as rubber is laid on the floor, the human body assumes an insulated condition, so that the potential is built up gradually. Hence, there is the possibility of the human body assuming the state of a high potential, with the result that there still remains the problem of safety.
In the arrangement of the prior art (3) in which a conductive member such as a chain is suspended from the apparatus, there is the problem that the grounding effect cannot be obtained if the apparatus is used on an insulating material such as rubber, in which case static electricity cannot be eliminated.
The arrangement of the prior art (4) is a generally adopted means in which an outer casing (such as a housing of an electric blower), i.e., a member which is disposed adjacent to an energized conductive material of the power source and has a sufficent grounding effect, is made conductive with the portion where static electricity is generated. In this arangement, the resistor is inserted to enhance reliability, as mentioned above, so as to ensure that only a very small current will flow if the outer casing of the electric blower is short-circuited due to the dielectric breakdown of the electric blower.
However, if the resistor is further short-circuited with the electric blower also being short-circuited, the status becomes such that a source voltage is directly applied to the dust case, involving the danger of electrification. Although the occurrence of such cases may be practically nil in terms of the probability; however, an element of danger still remains. In foreign countries, 220 V or 240 V is mainly used as the source voltage, which involves a high level of danger as compared with 100 V in the case of Japan. Hence, the adoption of this measure has been a problem in meeting such safety standards as Australiaa's SAA and West German VDE.
As described above, there have been problems in the prior art in terms of the handling features, reliability, safety, meeting the requirements of overseas standards, etc., and there have also been additional drawbacks in terms of productivity and production costs.